1. Field of the Invention
The present invention relates to the preparation of alkyl cyanoacetates, and, more especially, to the preparation of alkyl cyanoacetates by reacting the alkyl chloracetates with an alkali metal cyanide, notably sodium cyanide.
2. Description of the Prior Art
It is known to this art to prepare cyanoacetic esters by reacting an at least equimolar amount of a haloacetate with an alkali metal cyanide in an inert solvent, in the presence of hydrocyanic acid, at a temperature between 20.degree. and 250.degree. C. and under a pressure between 1 and 6 atmospheres. Compare French Pat. No. 1,447,526.
The hydrocyanic acid is not consumed during the reaction; rather, it serves to suppress any secondary reactions between the haloacetate and the already-formed cyano ester with attendant formation of by-products. According to this French Pat. No. 1,447,526 patent, it is particularly advantageous to use between 1.1 and 6 moles of haloacetate per mole of the alkali metal cyanide, and between 0.1 and 4 moles of HCN per mole of said alkali metal cyanide. The solvents suggested are principally alcohols corresponding to the alcohol moiety of the ester employed.
The principal disadvantage of this type of process is that, in order to utilize reaction velocities compatible with acceptable industrial production rates, it is necessary to conduct the reaction with solvent reflux. This poses severe safety problems, because under these conditions the toxic hydrocyanic acid is in the vapor phase.
It is also known to this art to prepare cyanoacetates by reacting sodium or potassium cyanide with a haloacetate; compare published French Patent Application No. 2,021,641. One characteristic of this process is the fact that the reaction is effected in acetonitrile using an excess of cyanide. According to the applicant, it is possible to conduct the reaction either in the presence or absence of water. It would also appear that the embodiment of conducting the process in the presence of water is industrially feasible only if the ester employed is derived from a tertiary alcohol; in fact, outside of these limits the hydrolysis of the ester function occurs to such extent as to be inconsistent with the economics of the process. But, if the reaction be carried out in the absence of water, it proceeds too slowly and the degree of conversion is quite poor.
Thus, serious need exists in this art for an improved process for cyanoacetate preparation that is not limited to one definite type of ester, that may be carried out at low temperatures under improved safety conditions, while at the same time permitting satisfactory reaction rates and degrees of conversion compatible with production on an industrial level.
See also U.S. Pat. No. 2,985,682; French Pat. Nos. 1,383,366, 1,447,526, 1,450,529, 2,021,641 and 2,357,533.